Optical detection of oscillating targets using modulation of scattered laser light

Abstract

The present invention provides systems and methods using a temporal-frequency sensitive receiver to detect laser light that is scattered by an oscillating object, thereby allowing remote monitoring of the object's position and movement.

1. A method for detecting an oscillating target, the method comprising:
 illuminating a measurement region using a pulsed laser beam; 
 collecting, for each of a plurality of ranges to one or more potential oscillating targets for which a return signal is present, a time series of return signals for that range; 
 computing a frequency-domain transform of each collected time series; and 
 analyzing the frequency-domain transform of each collected time series to determine whether modulation is present within a predetermined range of frequencies spanning an oscillation frequency associated with the oscillating target. 
 
   
   
     2. The method of  claim 1 , wherein a pulse repetition frequency of the pulsed laser beam substantially exceeds a Nyquist sampling frequency associated with the oscillation frequency. 
   
   
     3. The method of  claim 1 , wherein the oscillating target is one of a flying insect, a flying bird, a flying mammal, and a propeller-driven object. 
   
   
     4. The method of  claim 3 , wherein the flying insect is one of a fly, a bee, and a wasp, the oscillation frequency being produced by the beating of wings. 
   
   
     5. The method of  claim 4 , wherein the bee is a honeybee. 
   
   
     6. The method of  claim 3 , wherein the flying insect is trained or conditioned to locate a specific chemical. 
   
   
     7. The method of  claim 6 , wherein the specific chemical is associated with explosives. 
   
   
     8. The method of  claim 7 , wherein the explosives are associated with landmines. 
   
   
     9. The method of  claim 1 , wherein the frequency-domain transform is a Fourier transform. 
   
   
     10. The method of  claim 1 , wherein the oscillation frequency is greater than that of any wind-blown vegetation in the measurement region. 
   
   
     11. The method of  claim 1 , wherein the plurality of ranges are derived from measured times of flight of the pulsed laser beam. 
   
   
     12. A system for detecting an oscillating target, the system comprising:
 a pulsed laser to illuminate a measurement region; 
 an optical detector; 
 an optical receiving apparatus to collect return signals and feed the return signals to the optical detector, the optical detector producing an output signal; and 
 a computing device to receive the output signal from the optical detector, the computing device being configured to:
 collect, for each of a plurality of ranges to one or more potential oscillating targets for which a return signal is present, a time series of return signals for that range; 
 compute a frequency-domain transform of each collected time series; and 
 analyze the frequency-domain transform of each collected time series to determine whether modulation is present within a predetermined range of frequencies spanning an oscillation frequency associated with the oscillating target. 
 
 
   
   
     13. The system of  claim 12 , wherein the oscillating target is one of a flying insect, a flying bird, a flying mammal, and a propeller-driven object. 
   
   
     14. The system of  claim 13 , wherein the flying insect is one of a fly, a bee, and a wasp, the oscillation frequency being produced by the beating of wings. 
   
   
     15. The system of  claim 14 , wherein the bee is a honeybee. 
   
   
     16. The system of  claim 13 , wherein the flying insect is trained or conditioned to locate a specific chemical. 
   
   
     17. The system of  claim 16 , wherein the specific chemical is associated with explosives. 
   
   
     18. The system of  claim 17 , wherein the explosives are associated with landmines. 
   
   
     19. The system of  claim 12 , wherein the optical detector includes a photomultiplier tube.